1. Field of the Invention
The present invention relates to an optical element capable of separating light having different wavelengths, for use in optical communication, pickup apparatuses for use with optical disks, etc.
2. Description of Related Art
Due to the rapid spread of the Internet, there is a strong demand for an increase in the information transmission capacity of an optical fiber communication network. Under such a circumstance, wavelength division multiplexing (WDM) has been developed rapidly. The WDM is a communication technique of multiplexing independent information to transmit it, using light having a plurality of different wavelengths. According to this technique, in order to separate a signal that has been multiplexed, a wavelength separator having satisfactory wavelength selectivity is required.
As an element to be used as such a wavelength separator, a photonic crystal has been proposed (see, for example, JP-A-2002-236206). A photonic crystal is an artificially made crystal having a refractive index that is periodic with a period in the same order as the wavelength of light. A photonic crystal is categorized as one-dimensional, two-dimensional, or three-dimensional photonic crystal depending on the direction in which the photonic crystal has the periodicity of the refractive index. The two-dimensional and three-dimensional photonic crystals, which allow a three-dimensional waveguide structure to be provided, therefore have the effect of allowing a plurality of optical elements to be integrated in a limited size. However, two- or three-dimensional photonic structures are difficult to produce, since the structures have complexity.